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Mid range problem on YS 91FZ

Old 11-11-2007, 06:45 PM
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42etus
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Default Mid range problem on YS 91FZ

I've started having problems with my YS 91FZ engine. The idle is great. It'll idle for several minutes and go to full throttle with out skipping a beat. The top end is also great, plenty of power, smooth and steady. But at about 40 -60 % throttle the engine loads up and starts missing, smokes excessivly too. Going to full throttle, it stumbles, smokes and slowly clears itself out. It only runs good at half throttle for about 10 seconds b/4 it starts loading up.. I'm puzzled, as this engine has never done anything like this b/4, it's always been a sweet runner.
Info:
Prop - 14x7 Graupner
RPM - 9400
Fuel - Cool Power 30% Heli (22% oil)
Plug - OS F (New)
Altitude - 4300ft
I haven't tried adjusting the pressure regulator, since it's always run so well at the factory setting. This engine has had about 6 gallons of fuel through it and has never been sent to YS Service for any problems.
Any ideas.
Paul
Old 11-11-2007, 08:11 PM
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Troy Newman
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Default RE: Mid range problem on YS 91FZ

The regulator is too rich if the mid range is loading up. Adjust the Regulator Screw IN or CW to lean it start with about 1/4 turn and then you will have to reajust the other settings. Most importantly the the Low end air bleed screw will need to be adjusted. Since the regulator is rich then the low speed is likely too lean after you lean the regulator so I would expect to dial the air bleed screw IN (CW) to the richen the air bleed screw. Yes this means the air bleed screw works backward from the HS and the regulator and that is correct.

Adjust the regulator a little leaner and it should solve your problem once you get everything else setup again. Its close and some fine tuning is required.


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Old 11-11-2007, 08:32 PM
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42etus
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Default RE: Mid range problem on YS 91FZ

Thanks, Troy. I'll try adjusting the regulator next time I fly. Is there any reason it would go out of adjustment, since I haven't had this problem in the past?
Paul
Old 11-11-2007, 10:53 PM
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Troy Newman
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Default RE: Mid range problem on YS 91FZ

Well yes and no. First off temperature changes. As it gets cooler or hotter. things will change.

Another thing thinking about it try changing the glow plug first. Since all has been working well and it is not loading up...this is usually sign of a bad glow plug. Plus you may be a little on the rich side....this with the glow plug going south would be the issue.

My first step is to change the plug...if this doesn't solve it then adjust the regulator...

Also things can change with time...the regulator is a little silicone plunger, with a silicone diaphram and a spring. A little bit of dirt or debris in the regulator can keep the plunger from closing all the way this would act to make it too rich as the plunger is not closing off properly. Also the diaphram could become deformed a little not that it would need replacing but enough to change the settings...Then there is the spring that the regulator screw puts compression on to hold that plunger closed at the right times. Any of these little parts can change and the setting would then change but a little.

Do the new plug first.

OS #F or YS plugs only please.

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Old 11-12-2007, 10:59 AM
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Default RE: Mid range problem on YS 91FZ

The first thing I did was install a new plug. (OS #F). No change. Next I'll try leaning the regulator by screwing it in by quarter turn increments. Would you suggest disassembing the regulator and cleaning it or would that be opening up a can of worms?
Thanks Troy,
Paul
Old 11-12-2007, 12:11 PM
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Troy Newman
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Default RE: Mid range problem on YS 91FZ

Not yet try adjusting it. If it only takes a little bit of work in resetting things it will be worth it.

However write down everything you do...This way if it doesn't solve it then you can open it up and clean it out and put everythign abck where it was suppose to be from before.

Likely 1/4 turn will make the difference....then you can fine tune it from there. You should not have to go more than about 1/2 turn maybe 3/4 so once it starts getting close....finer adjustments may be needed. 1/4 turn to start with is a good guess. It should make a difference.

I always keep a log book on the changes I make.


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